MSIX is a modern Windows app package format, a successor of APPX and a "spiritual successor" to some other - now legacy - formats, including but not limited to MSI, App-V and ClickOnce.
Apps deployed as MSIX packages benefit from several out-of-the-box features and properties, including:
Fast and reliable installation, clean uninstallation,
Content delivery optimizations, ensuring faster downloads with minimum impact and network bandwidth usage,
Access to various modern Windows APIS which are not available for classically deployed win32 apps,
Extensibility and shimming thanks to Package Support Framework,
Add-ons and modification packages,
Easy switch to MSIX app attach,
Distribution and monetization in Microsoft Store.
And best of all, the big part of the ecosystem is open-sourced and the core support for MSIX deployment is built-in in any computer running still supported version of Windows 10. Although the format is relatively young, there already exist several package authoring tools, both from Microsoft and ISVs, and the community is constantly growing.
MSIX Hero - the ultimate MSIX toolkit for IT Pros.